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<!DOCTYPE html><html lang="en"><head><meta charset="utf-8"><meta name="viewport" content="width=device-width, initial-scale=1.0"><meta name="generator" content="rustdoc"><meta name="description" content="A one-shot channel is used for sending a single message between asynchronous tasks. The [`channel`] function is used to create a [`Sender`] and [`Receiver`] handle pair that form the channel."><meta name="keywords" content="rust, rustlang, rust-lang, oneshot"><title>tokio::sync::oneshot - Rust</title><link rel="preload" as="font" type="font/woff2" crossorigin href="../../../SourceSerif4-Regular.ttf.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../../../FiraSans-Regular.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../../../FiraSans-Medium.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../../../SourceCodePro-Regular.ttf.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../../../SourceSerif4-Bold.ttf.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../../../SourceCodePro-Semibold.ttf.woff2"><link rel="stylesheet" type="text/css" href="../../../normalize.css"><link rel="stylesheet" type="text/css" href="../../../rustdoc.css" id="mainThemeStyle"><link rel="stylesheet" type="text/css" href="../../../ayu.css" disabled><link rel="stylesheet" type="text/css" href="../../../dark.css" disabled><link rel="stylesheet" type="text/css" href="../../../light.css" id="themeStyle"><script id="default-settings" ></script><script src="../../../storage.js"></script><script src="../../../crates.js"></script><script defer src="../../../main.js"></script>
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</a><h2 class="location">Module oneshot</h2><div class="sidebar-elems"><div class="block items"><ul><li><a href="#modules">Modules</a></li><li><a href="#structs">Structs</a></li><li><a href="#functions">Functions</a></li></ul></div><div id="sidebar-vars" data-name="oneshot" data-ty="mod" data-relpath="./"></div><script defer src="./sidebar-items.js"></script></div></nav><main><div class="width-limiter"><div class="sub-container"><a class="sub-logo-container" href="../../../tokio/index.html"><img class="rust-logo" src="../../../rust-logo.png" alt="logo"></a><nav class="sub"><div class="theme-picker"><button id="theme-picker" aria-label="Pick another theme!" aria-haspopup="menu" title="themes"><img width="18" height="18" alt="Pick another theme!" src="../../../brush.svg"></button><div id="theme-choices" role="menu"></div></div><form class="search-form"><div class="search-container"><div><select id="crate-search"><option value="All crates">All crates</option></select><input class="search-input" name="search" autocomplete="off" spellcheck="false" placeholder="Click or press ‘S’ to search, ‘?’ for more options…" type="search"></div><button type="button" id="help-button" title="help">?</button><a id="settings-menu" href="../../../settings.html" title="settings"><img width="18" height="18" alt="Change settings" src="../../../wheel.svg"></a></div></form></nav></div><section id="main-content" class="content"><h1 class="fqn"><span class="in-band">Module <a href="../../index.html">tokio</a>::<wbr><a href="../index.html">sync</a>::<wbr><a class="mod" href="#">oneshot</a><button id="copy-path" onclick="copy_path(this)" title="Copy item path to clipboard"><img src="../../../clipboard.svg" width="19" height="18" alt="Copy item path"></button></span><span class="out-of-band"><span id="render-detail"><a id="toggle-all-docs" href="javascript:void(0)" title="collapse all docs">[<span class="inner">−</span>]</a></span><a class="srclink" href="../../../src/tokio/sync/oneshot.rs.html#1-1366" title="goto source code">[src]</a></span></h1><details class="rustdoc-toggle top-doc" open><summary class="hideme"><span>Expand description</span></summary><div class="docblock"><p>A one-shot channel is used for sending a single message between
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asynchronous tasks. The <a href="fn.channel.html" title="channel"><code>channel</code></a> function is used to create a
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<a href="struct.Sender.html" title="Sender"><code>Sender</code></a> and <a href="struct.Receiver.html" title="Receiver"><code>Receiver</code></a> handle pair that form the channel.</p>
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<p>The <code>Sender</code> handle is used by the producer to send the value.
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The <code>Receiver</code> handle is used by the consumer to receive the value.</p>
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<p>Each handle can be used on separate tasks.</p>
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<p>Since the <code>send</code> method is not async, it can be used anywhere. This includes
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sending between two runtimes, and using it from non-async code.</p>
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<h2 id="examples" class="section-header"><a href="#examples">Examples</a></h2>
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<div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="kw">use</span> <span class="ident">tokio::sync::oneshot</span>;
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<span class="attribute">#[<span class="ident">tokio::main</span>]</span>
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<span class="kw">async</span> <span class="kw">fn</span> <span class="ident">main</span>() {
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<span class="kw">let</span> (<span class="ident">tx</span>, <span class="ident">rx</span>) <span class="op">=</span> <span class="ident">oneshot::channel</span>();
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<span class="ident">tokio::spawn</span>(<span class="kw">async</span> <span class="kw">move</span> {
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<span class="kw">if</span> <span class="kw">let</span> <span class="prelude-val">Err</span>(<span class="kw">_</span>) <span class="op">=</span> <span class="ident">tx</span>.<span class="ident">send</span>(<span class="number">3</span>) {
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<span class="macro">println!</span>(<span class="string">"the receiver dropped"</span>);
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}
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});
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<span class="kw">match</span> <span class="ident">rx</span>.<span class="kw">await</span> {
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<span class="prelude-val">Ok</span>(<span class="ident">v</span>) => <span class="macro">println!</span>(<span class="string">"got = {:?}"</span>, <span class="ident">v</span>),
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<span class="prelude-val">Err</span>(<span class="kw">_</span>) => <span class="macro">println!</span>(<span class="string">"the sender dropped"</span>),
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}
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}</code></pre></div>
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<p>If the sender is dropped without sending, the receiver will fail with
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<a href="error/struct.RecvError.html" title="error::RecvError"><code>error::RecvError</code></a>:</p>
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<div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="kw">use</span> <span class="ident">tokio::sync::oneshot</span>;
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<span class="attribute">#[<span class="ident">tokio::main</span>]</span>
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<span class="kw">async</span> <span class="kw">fn</span> <span class="ident">main</span>() {
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<span class="kw">let</span> (<span class="ident">tx</span>, <span class="ident">rx</span>) <span class="op">=</span> <span class="ident">oneshot::channel</span>::<span class="op"><</span><span class="ident">u32</span><span class="op">></span>();
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<span class="ident">tokio::spawn</span>(<span class="kw">async</span> <span class="kw">move</span> {
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<span class="ident">drop</span>(<span class="ident">tx</span>);
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});
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<span class="kw">match</span> <span class="ident">rx</span>.<span class="kw">await</span> {
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<span class="prelude-val">Ok</span>(<span class="kw">_</span>) => <span class="macro">panic!</span>(<span class="string">"This doesn't happen"</span>),
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<span class="prelude-val">Err</span>(<span class="kw">_</span>) => <span class="macro">println!</span>(<span class="string">"the sender dropped"</span>),
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}
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}</code></pre></div>
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<p>To use a oneshot channel in a <code>tokio::select!</code> loop, add <code>&mut</code> in front of
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the channel.</p>
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<div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="kw">use</span> <span class="ident">tokio::sync::oneshot</span>;
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<span class="kw">use</span> <span class="ident">tokio::time</span>::{<span class="ident">interval</span>, <span class="ident">sleep</span>, <span class="ident">Duration</span>};
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<span class="attribute">#[<span class="ident">tokio::main</span>]</span>
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<span class="kw">async</span> <span class="kw">fn</span> <span class="ident">main</span>() {
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<span class="kw">let</span> (<span class="ident">send</span>, <span class="kw-2">mut</span> <span class="ident">recv</span>) <span class="op">=</span> <span class="ident">oneshot::channel</span>();
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<span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">interval</span> <span class="op">=</span> <span class="ident">interval</span>(<span class="ident">Duration::from_millis</span>(<span class="number">100</span>));
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<span class="ident">tokio::spawn</span>(<span class="kw">async</span> <span class="kw">move</span> {
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<span class="ident">sleep</span>(<span class="ident">Duration::from_secs</span>(<span class="number">1</span>)).<span class="kw">await</span>;
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<span class="ident">send</span>.<span class="ident">send</span>(<span class="string">"shut down"</span>).<span class="ident">unwrap</span>();
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});
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<span class="kw">loop</span> {
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<span class="macro">tokio::select!</span> {
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<span class="kw">_</span> <span class="op">=</span> <span class="ident">interval</span>.<span class="ident">tick</span>() => <span class="macro">println!</span>(<span class="string">"Another 100ms"</span>),
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<span class="ident">msg</span> <span class="op">=</span> <span class="kw-2">&mut</span> <span class="ident">recv</span> => {
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<span class="macro">println!</span>(<span class="string">"Got message: {}"</span>, <span class="ident">msg</span>.<span class="ident">unwrap</span>());
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<span class="kw">break</span>;
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}
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}
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}
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}</code></pre></div>
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<p>To use a <code>Sender</code> from a destructor, put it in an <a href="https://doc.rust-lang.org/1.59.0/core/option/enum.Option.html" title="Option"><code>Option</code></a> and call
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<a href="https://doc.rust-lang.org/1.59.0/core/option/enum.Option.html#method.take" title="Option::take"><code>Option::take</code></a>.</p>
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<div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="kw">use</span> <span class="ident">tokio::sync::oneshot</span>;
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<span class="kw">struct</span> <span class="ident">SendOnDrop</span> {
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<span class="ident">sender</span>: <span class="prelude-ty">Option</span><span class="op"><</span><span class="ident">oneshot::Sender</span><span class="op"><</span><span class="kw-2">&</span><span class="lifetime">'static</span> <span class="ident">str</span><span class="op">></span><span class="op">></span>,
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}
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<span class="kw">impl</span> <span class="ident">Drop</span> <span class="kw">for</span> <span class="ident">SendOnDrop</span> {
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<span class="kw">fn</span> <span class="ident">drop</span>(<span class="kw-2">&mut</span> <span class="self">self</span>) {
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<span class="kw">if</span> <span class="kw">let</span> <span class="prelude-val">Some</span>(<span class="ident">sender</span>) <span class="op">=</span> <span class="self">self</span>.<span class="ident">sender</span>.<span class="ident">take</span>() {
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<span class="comment">// Using `let _ =` to ignore send errors.</span>
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<span class="kw">let</span> <span class="kw">_</span> <span class="op">=</span> <span class="ident">sender</span>.<span class="ident">send</span>(<span class="string">"I got dropped!"</span>);
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}
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}
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}
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<span class="attribute">#[<span class="ident">tokio::main</span>]</span>
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<span class="kw">async</span> <span class="kw">fn</span> <span class="ident">main</span>() {
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<span class="kw">let</span> (<span class="ident">send</span>, <span class="ident">recv</span>) <span class="op">=</span> <span class="ident">oneshot::channel</span>();
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<span class="kw">let</span> <span class="ident">send_on_drop</span> <span class="op">=</span> <span class="ident">SendOnDrop</span> { <span class="ident">sender</span>: <span class="prelude-val">Some</span>(<span class="ident">send</span>) };
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<span class="ident">drop</span>(<span class="ident">send_on_drop</span>);
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<span class="macro">assert_eq!</span>(<span class="ident">recv</span>.<span class="kw">await</span>, <span class="prelude-val">Ok</span>(<span class="string">"I got dropped!"</span>));
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}</code></pre></div>
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</div></details><h2 id="modules" class="small-section-header"><a href="#modules">Modules</a></h2>
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<div class="item-table"><div class="item-row"><div class="item-left module-item"><a class="mod" href="error/index.html" title="tokio::sync::oneshot::error mod">error</a></div><div class="item-right docblock-short"><p>Oneshot error types.</p>
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</div></div></div><h2 id="structs" class="small-section-header"><a href="#structs">Structs</a></h2>
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<div class="item-table"><div class="item-row"><div class="item-left module-item"><a class="struct" href="struct.Receiver.html" title="tokio::sync::oneshot::Receiver struct">Receiver</a></div><div class="item-right docblock-short"><p>Receives a value from the associated <a href="struct.Sender.html" title="Sender"><code>Sender</code></a>.</p>
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</div></div><div class="item-row"><div class="item-left module-item"><a class="struct" href="struct.Sender.html" title="tokio::sync::oneshot::Sender struct">Sender</a></div><div class="item-right docblock-short"><p>Sends a value to the associated <a href="struct.Receiver.html" title="Receiver"><code>Receiver</code></a>.</p>
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</div></div></div><h2 id="functions" class="small-section-header"><a href="#functions">Functions</a></h2>
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<div class="item-table"><div class="item-row"><div class="item-left module-item"><a class="fn" href="fn.channel.html" title="tokio::sync::oneshot::channel fn">channel</a></div><div class="item-right docblock-short"><p>Creates a new one-shot channel for sending single values across asynchronous
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tasks.</p>
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